If some TAs want to work and others do not, can I reallocate work to the available TAs?

Potentially, yes, within limits.  TA duties are outlined in the work agreements completed and signed by departments/faculty and TAs at the beginning of the semester.  Duties must fall within the established work agreements.  Faculty must also be cognizant of the number of hours of the TA appointment and cannot assign work that would exceed the appointment hours outlined in the agreements.  Faculty must also honor TAs’ right to strike and cannot be perceived as exerting any pressure on TAs with respect to the strike.